1. Field of the Invention
This invention relates to a developing apparatus which can be used in an image forming apparatus such as an electrophotographic copying apparatus or an electrophotographic printer.
2. Related Background Art
Heretofore, an image forming apparatus using, for example, an electrophotographic system has been provided with, for example, a rotatable drum-like electrophotographic photosensitive body, i.e., a photosensitive drum, as an image bearing body, in substantially the central portion thereof, and charging means uniformly charges the surface thereof. Thereafter, the surface of the photosensitive body is subjected to exposure and an electrostatic latent image corresponding to an image signal is formed on that surface. This electrostatic latent image comes to a position opposed to a developing apparatus with the rotation of the photosensitive body, and is visualized by a developer, and a so-called toner image is formed on the photosensitive body. Thereafter, this toner image is electrostatically transferred onto a recording material by transferring means and further, is fixed by heat and pressure in a fixing device, whereby a permanent image is formed on the recording material. A cleaning device for removing any toner or the like remaining on the photosensitive body after the termination of the transfer is disposed at a desired location.
As the developing apparatus in the image forming apparatus adopting the construction as schematically described above, various ones using a dry type monocomponenet developer as the developer have been proposed and put into practical use. Particularly, there is known a developing apparatus using only non-magnetic toner particles (hereinafter simply referred to as the "toner") as the dry type monocomponent developer.
Such a developing apparatus is provided with a rotatable sleeve-like developer bearing body, i.e., a developing sleeve, in order to carry the toner to a developing position opposed to the photosensitive drum, make the toner adhere to the electrostatic latent image on the photosensitive drum and form a toner image thereon. In any developing apparatuses, however, it is not easy to form a thin layer of the monocomponenet developer, i.e., the toner, on the developing sleeve, and it is a main point in the image forming operation.
Nowadays, improvements in the resolution, clearness, etc. of an image formed by the image forming apparatus have been further required, and in the developing apparatus as described above, there have been made various proposals regarding a method of forming a thin layer of toner on the developing sleeve and a developing apparatus embodying it.
For example, in a developing apparatus disclosed in Japanese Patent Application Laid-Open No. 54-43038, an elastic blade as developer layer thickness regulating means made of rubber or a metal is made to be abutted against the surface of the developing sleeve. That is, the toner is made to pass through the abutting portion of contact between this elastic blade and the developing sleeve and the layer thickness of the toner is regulated to thereby form a thin layer of the toner on the developing sleeve and, in this abutting portion, triboelectricity (frictional charging amount) sufficient for development is imparted to the toner.
In the prior art as described above, to regulate nonmagnetic toner particles by the elastic blade, means for supplying the toner onto the developing sleeve becomes separately necessary. That is, as is heretofore known, in the case of a developing apparatus using magnetic toner particles as a monocomponent developer, it is possible to supply the toner onto a developing sleeve by a magnetic force produced by a magnet provided in the developing sleeve, whereas this is impossible in the case of a developing apparatus using nonmagnetic toner particles.
So, in order to effect the supply of the toner to the developing sleeve, it has been variously proposed to make a roller-like member having elasticity using a foamed rubber material such as polyurethane foam or sponge or a brush material abut against the developing sleeve. FIG. 9 of the accompanying drawings shows an example of the prior art developing apparatus using a monocomponent developer.
The developing apparatus 4 contains non-magnetic toner particles (toner) in a developing container 41, and a portion of that side of the developing container 41 on which the developing apparatus 4 and a photosensitive drum 1 are opposed to each other opens, and in such a manner as to expose a circumferential portion from this opening portion, a developing sleeve 42 as a developer bearing body is supported on the developing container 41 for rotation in the direction of arrow B. Also, spacers (not shown) as gap regulating members are provided on the lengthwisely opposite end portions of the developing sleeve 42, and these spacers abut against the surface of the photosensitive drum 1, whereby the surface of the photosensitive drum 1 and the surface of the developing sleeve 42 are opposed to each other with a predetermined distance therebetween.
An elastic blade 44 as developer layer thickness regulating means for regulating the quantity of toner abutted on the surface of the developing sleeve 42 bears against the developing sleeve 42, and at a position upstream of this elastic blade 44 with respect to the direction of rotation of the developing sleeve 42, an elastic roller 43 as developer supplying and scraping means abuts against the developing sleeve 42.
When the developing apparatus 4 starts its developing operation, the toner is agitated by the rotation of an agitating member 45 in the direction of arrow C and is carried to the elastic roller 43 side. The toner is borne on the surface of the developing sleeve 42 while being preliminarily charged by the friction thereof with the elastic roller 43 rotated in the direction of arrow D, whereafter the toner is carried to the abutting portion between the elastic blade 44 and the developing sleeve 42 with the rotation of the developing sleeve 42, and has its layer thickness regulated and becomes a thin layer. By the friction at this time, desired charging is imparted to the toner.
Thereafter, the toner borne and carried to a developing position opposed to the photosensitive drum 1 with the rotation of the developing sleeve 42 flies onto the photosensitive drum 1 by a developing bias voltage applied to the developing sleeve 42, and selectively adheres to the electrostatic latent image on the surface of the photosensitive drum to thereby form a toner image. Any toner remaining on the surface of the developing sleeve 42 without contributing to development is again carried into the developing container 41 by the rotation of the developing sleeve 42, and is scraped off by the elastic roller 43, whereby it is mixed with the toner in the developing container 41.
When in such a prior art developing apparatus, a metal material is used as the developing sleeve 42, if a blade made of a metallic thin plate is used as the elastic blade 44, it will abrade the developing sleeve 42, and this is not preferable. To obtain a good thin layer of toner, it is necessary to use a rubber material such as urethane or silicone rubber.
By adopting the construction schematically described above, it has become possible to well effect the formation of a thin layer of toner on the developing sleeve 42.
However, a developing apparatus using nonmagnetic toner particles (toner), unlike a developing apparatus using magnetic toner particles, cannot utilize a magnetic adsorbing force and therefore, cannot powerfully hold the toner on the developing sleeve 42. Accordingly, it is difficult to prevent the leakage of the toner to the outside of the developing apparatus 4.
That is, the other toner than the toner which has slipped out of the portion of pressure contact between the elastic blade 44 and the developing sleeve 42 and has been sufficiently charged has no adsorbing force enough for the developing sleeve 42 to the able to hold and therefore, the toner leaks out from the lower portion and the vicinity of the lengthwisely opposite end portions of the developing sleeve 42, and so-called toner leakage becomes liable to occur, and this is liable to cause the problem of contaminating the interior of the image forming apparatus by the toner.
Therefore, a flexible developer sealing member 46 abutting against the developing sleeve 42 with light pressure is provided on a lower frame 48 located in the opening portion of the bottom of the developing container 41 to thereby permit the passage of the toner carried again into the developing container 41 without contributing to development, and also prevent the toner in the developing container 41 from leaking out from the lower portion of the developing container 41.
The developing apparatus as described above is used in an image forming apparatus such as a compact copying apparatus or a page printer, but an apparatus in which a developing apparatus is made into a unit or process means including at least the developing apparatus and an image bearing body are integrally made into a cartridge which is detachably attachable to the main body of an image forming apparatus and can be interchanged has heretofore been put into practical use.
According to this process cartridge system, the maintenance of the apparatus can be done by a user himself without resorting to a serviceman and therefore, the operability of the apparatus can be markedly improved. However, the developing apparatus made into a unit or a process cartridge may suffer from the possibility of the toner leaking out by a light shock or the like applied thereto during the interchange thereof and therefore, various kinds of sealing are provided in the developing apparatus. Particularly, the above-described developer sealing member 46 effectively serves to prevent the leakage of the developer.
FIG. 10 of the accompanying drawings shows the developing position of the prior art developing apparatus 4 as it is seen from the photosensitive drum 1 side. For the convenience of illustrating the sealing of the toner, the developing sleeve 42 is not shown. Also, there is shown a developing area G which is a toner image forming area on the photosensitive drum 1.
As will be understood from FIGS. 9 and 10, a developer sealing member 46 which is in the form of a strip type sheet wider than the developing area G of the developing sleeve 42 is provided in the lower position of the opening portion of the developing container 41, and the lower frame 48 of the developing container lengthwisely fixes one end of the developer sealing member 46 which is adjacent to the photosensitive drum 1. Also, the free end of the developer sealing member 46 contacts with and frictionally slides on the developing sleeve 42 by its own elasticity in such a manner as to be along the direction of rotation of the developing sleeve 42.
As the material of the developer sealing member 46, use is made of thin urethane rubber, film-like polycarbonate of weak rigidity, PET or the like. During the collection of the toner which has not contributed to development, the developer sealing member 46 falls down inwardly of the developing apparatus as indicated by arrow E in FIG. 9 and does not hinder the collection of the toner. Against the blowing-out of the toner from the interior of the developing apparatus 4, the developer sealing member 46 comes into close contact with the developing sleeve 42 to thereby prevent the leakage of the toner.
Further, in the prior art developing container 41, in order to prevent the leakage of the toner from the lengthwisely opposite end portions of the developing sleeve 42, end portion peripheral surface sealing members 47 are provided in the inner portions opposite to the opening portion of the developing container 41 on the lengthwisely opposite end portions of the developing sleeve 42 which are outer than the developing area G, to thereby prevent the outflow of the toner to the outside of the developing area G.
Heretofore, as described above, as the end portion peripheral surface sealing members 47, use has been slidely made of ones having the surfaces thereof formed of felt or electrostatically implanted hair or the like and having the base material thereof formed by an elastic member, and as shown in FIGS. 9 and 10, the end portion peripheral surface sealing members 47 are urged against the outer peripheral surface of the developing sleeve 42 to thereby prevent the outflow of the toner.
In the prior art developing apparatus 4, however, on the lengthwisely opposite end portions of the developing sleeve 42, the developing sleeve 42 is designed to frictionally slide in close contact with the developer sealing member 46 in such a manner as to sandwich the latter between the end portion peripheral surface sealing member 47 and the developing sleeve 42. Therefore, a pull force in the direction of rotation of the developing sleeve 42 is applied to the developer sealing member 46, and by this force, the developer sealing member 46 is waved and accordingly, if the developing operation is repeated a number of times, there will arise the problem that the leakage of the toner occurs.
So, as a solution for this problem, from the viewpoint of decreasing the pull force applied to the developer sealing member 46, it is conceivable to reduce the area overlapping the developer sealing member 46 on the end portion peripheral surface sealing members 47 to prevent the waving of the developer sealing member 46.
However, if the overlapping area between the developer sealing member 46 and the end portion peripheral surface sealing members 47 is inadvertently decreased, a reduction in sealing performance will result in the lengthwisely opposite end portions of the lower frame 48 of the opening portion of the developing container 41 and after all, the leakage of the toner will occur from these portions.
As described above, the setting of the overlapping area between the developer sealing member 46 and the end portion peripheral surface sealing members 47 is delicately and sensitively concerned with the leakage of the toner.